1. Field of the Invention
The present invention relates to an electrically operated power assist apparatus for a manually operated vehicle, such as a bicycle, and, more particularly, to a new and novel construction of a power assist apparatus for a bicycle.
2. Description of the Related Art
By way of background, FIG. 1 illustrates a standard bicycle which includes a front steering wheel 50 and a rear wheel 60, which may be attached to a frame 20. The frame has a head tube 32 which journals a front fork 52 for steering via handles bars 33 by a rider of the bicycle 100. A seat tube 21 is carried by the frame 20 adjacent the rear wheel 60 and a seat post, upon which a saddle type seat 25 is positioned thereon to accommodate a rider, is slidably received in the seat tube 21 for adjusting the height of the seat 25.
In the standard bicycle 100, a horizontally oriented crank journal 113 is positioned beneath the seat tube 21 for supporting a rider-propelled drive mechanism 120. The drive mechanism 120 generally comprises a crank arm 123 having a first end journalled to each side of the crank journal 113 and an opposite second end rotatably supporting a pedal 25. A chain sprocket 129 having a plurality of circumferential teeth is fixedly secured to the crank journal 113. A chain 140 is wrapped around the chain sprocket 129 and a rear sprocket 150 mounted to the rear wheel 60, whereby application of power by the rider on the pedals 25 rotates the sprockets 129, 150, and hence the rear wheel 60, to propel the bicycle 100. A derailleur (not shown) is often substituted from the single rear sprocket 150, and may have a plurality of sprockets to provide variable gearing for rider comfort and efficiency when encountering variable terrain.
Bicycles have been utilized as a means of transportation for over one hundred years. From an environmental standpoint, bicycles are preferable to automobiles and motorcycles because they are non-polluting. However, some people are deterred from using a bicycle due to the effort required to pedal up one or more inclines, or hills. Therefore, if a power assist device was incorporated into a bicycle with a minimum degree of difficulty and expense, then people would be more inclined to use a bicycle as a means of travel, especially for short trips, since the overall physical effort to propel the bicycle would be minimal.
Electric powered bicycles are known in the art, for example, as illustrated in U.S. Pat. Nos. 3,431,994 and 3,921,745. These types of electric powered bicycles incorporate an electric motor which is powered by one or more batteries. Typically, the motor operates through a drive wheel which frictionally engages with one of the wheels of the bicycle. Other methods include different configurations of direct drive systems, involving shafts, chains, and gears, but with the common feature of the driving motor being mounted on the bicycle frame in one position or another (e.g. near the pedaling sprocket, on one of the stays or on a rack above the rear wheel).
However, the prior art direct drive power assist devices for a bicycle have generally required complex gearing arrangements. Upon removal of the wheel for maintenance, such as tire repair, precise reengagement of the direct drive device is difficult, leading to excessive wear and noise during operation. Also, complex gearing arrangements are difficult to maintain in precise alignment when the bicycle encounters road bumps and holes. Further, the prior art direct drive power assist devices for bicycles have not been designed to be readily removable from the bicycle to permit normal manual usage without the extra weight of the direct drive device.
Accordingly, there is a need in the art for a modular power assist device for a bicycle that can be easily added to or removed from the bicycle, and which efficiently transmits torque to the crank journal without excessive noise or gear tooth wear due to misalignment.